Chemical senses – gustation (taste) and olfaction (smell) Their chemoreceptors respond to chemicals in aqueous solution Taste – to substances dissolved in saliva Smell – to substances dissolved in fluids of the nasal membranes

Sense of Smell The organ of smell is the olfactory epithelium, which covers the superior nasal concha Olfactory receptor cells are neurons with radiating olfactory cilia Olfactory receptors are surrounded and cushioned by supporting cells

Olfactory Receptors Figure 15.21

Sense of Taste--Taste Buds Taste is 80% smell Most of the 10,000 or so taste buds are found on the tongue Taste buds are found in papillae of the tongue mucosa 2 types of epithelial cells: Gustatory (taste cells)—gustatory hairs (sensitive) Basal cells (stem cells for quick replacement-- 7-10 days)

In order to be tasted, a chemical: Physiology of Taste In order to be tasted, a chemical: Must be dissolved in saliva Must contact gustatory hairs Binding of the food chemical: Depolarizes the taste cell membrane, releasing neurotransmitters Initiates a generator potential that elicits an action potential

Taste Buds Figure 15.23

There are five basic taste sensations Sweet – sugars, saccharin, alcohol, and some amino acids Salty – metal ions Sour – hydrogen ions Bitter – alkaloids such as quinine and nicotine Umami- amino acids “beef taste”

Influence of Other Sensations on Taste Temperature and texture enhance or detract from taste A lot of what we smell is based on pain sensors (Chili peppers, ammonia, etc.)

Aging: Chemical senses – few problems occur until the fourth decade, when these senses begin to decline

Chunk and Chew: Partner A: Partner B: Please explain what is needed for smell to occur and describe the pathway from odor molecules to the brain. Partner B: Please explain the two types of epithelial cells found in taste buds that make the process of taste happen. Also, describe the pathway of taste molecules from the tongue to the brain.